A diffusion method for improving the magnetic properties of sintered magnets and high-performance sintered NdFeB magnets prepared thereby

Abstract

The application discloses a diffusion method for improving the magnetic property of a sintered magnet, which comprises the following steps: covering a carbon film on the surface of a sintered NdFeB magnet substrate, wherein the mass ratio of the carbon film to the magnet substrate is 0.2% to 2.0%; performing magnetron sputtering film coating on the magnet substrate coated with the carbon film to coat a heavy rare earth film, wherein the mass ratio of the heavy rare earth to the magnet substrate is 0.2% to 4%, and a film-coated magnet is obtained; and performing grain boundary diffusion treatment on the film-coated magnet to obtain a high-performance sintered NdFeB magnet after the grain boundary diffusion treatment. The application further discloses the high-performance sintered NdFeB magnet prepared by the method. The application can reduce the Br reduction amount and improve the diffusion effect of the heavy rare earth at the same time by covering a carbon film on the surface of the magnet and controlling the weight of the carbon, and finally a rare earth NdFeB magnet with high Br and high Hcj magnetic property can be obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to a diffusion method for improving the magnetic properties of sintered magnets and the high-performance sintered NdFeB magnets prepared thereby. BACKGROUND

[0002] Sintered NdFeB magnet materials have high magnetic properties, do not contain strategic metal nickel, are relatively low in price, have a wide range of applications, and have a long service life, and thus have a wide development prospect.

[0003] However, sintered NdFeB magnets are still in the development stage. First, the magnetic properties of sintered NdFeB magnets have a lot of room for improvement. The magnetic energy product of the current sintered NdFeB magnets can only reach 83% of the theoretical value, and the magnetic energy product obtained by industrial small-batch production and large-batch production is even lower. Second, the actual sintered Hcj is only 20% to 30% of the theoretical value, and there is still a lot of room for improvement. Therefore, it is particularly important to improve the magnetic properties of sintered NdFeB magnets.

[0004] Diffusion technology is a technology that can quickly improve Hcj in recent years, which has the advantages of low cost, easy operation, and high cost performance. However, there are problems of insufficient diffusion depth of heavy rare earth and diffusion of heavy rare earth to the main phase during the diffusion process, resulting in a large decrease in the Br of the magnet after diffusion and an insufficient increase in Hcj. Therefore, how to better improve the diffusion effect of sintered NdFeB is particularly important. SUMMARY

[0005] The present application provides a diffusion method for improving the magnetic properties of sintered magnets by pre-diffusing a layer of carbon to better improve the diffusion effect.

[0006] The method of the present application can obtain NdFeB magnets with higher magnetic properties compared to conventional diffusion processes.

[0007] The technical solution adopted by the present application is as follows:

[0008] A diffusion method for improving the magnetic properties of sintered magnets, the method comprising the following steps:

[0009] (1) A layer of carbon film is coated on the surface of the sintered NdFeB magnet substrate using a multi-arc sputtering method, the thickness of the carbon film is 2-20 um (preferably 5-12 um), and the mass fraction is 0.2%-2.0% (preferably 0.89%-1.15%) of the magnet substrate. The magnet substrate coated with the carbon film is subjected to magnetron sputtering film plating to plate a heavy rare earth film, the thickness of the heavy rare earth film layer is 1 um-30 um (preferably 5-25 um), and the mass fraction of the heavy rare earth is 0.2%-4% (preferably 0.5%-3.0%) of the magnet substrate, to obtain a plated magnet;

[0010] (2) coating magnet is treated by grain boundary diffusion, diffusion temperature is 800-1000℃ (preferably 850-920℃), diffusion time is 1-48h (preferably 6-12h), vacuum degree is above 1.0*10-3Pa, after grain boundary diffusion, the magnet is cooled to room temperature and then is tempered to obtain high-performance sintered NdFeB magnet after grain boundary diffusion.

[0011] In the step (1), the heavy rare earth is Tb or Dy.

[0012] In the step (1), the mass ratio of the carbon film is preferably 0.89%-1.15% of the magnet substrate.

[0013] In the step (1), the mass ratio of the heavy rare earth is preferably 0.5%-3.0% of the magnet substrate, more preferably 1.7%-2.4%.

[0014] In the step (1), the PVD target material of the multi-arc sputtering method is graphite target material, and the atmosphere is high-purity Ar.

[0015] In the step (1), the magnetron sputtering coating is carried out by physical vapor deposition using a plasma vacuum coating machine, the atmosphere source is high-purity Ar, the cavity vacuum degree is between 0.3-0.5pa, the internal working temperature is 100-150℃, the obtained film thickness is between 1um-30um, and the mass ratio of the heavy rare earth is 0.2%-4% of the magnet substrate.

[0016] In the step (1), the sintered NdFeB magnet substrate can be selected from various types or grades of sintered NdFeB magnets, the main components are Nd, Fe, Pr, B, and can also contain other various elements such as rare earth elements Ho, Gd, Dy, Tb, or other metal or non-metal elements such as Al, Cu, Zn, Sn, In, Ti, V, Co, Mn, Ni, Ca, Zr, Ga, Nb, Mo, Si, etc., the element composition and component ratio of the magnet substrate have no effect on the diffusion process of the present application.

[0017] In the step (2), the carbon content in the high-performance sintered NdFeB magnet after grain boundary diffusion is 0.05%-0.30wt%, and the content of heavy rare earth is 0.11%-4%.

[0018] Generally, when the sintered NdFeB magnet substrate does not contain carbon elements, the carbon film covered in step (1) is the source of carbon elements in the final diffused magnet, the mass ratio of the carbon film is 0.2%-2.0% of the magnet substrate, and the carbon content in the diffused magnet is 0.05wt%-0.3wt%.

[0019] When the sintered NdFeB magnet substrate does not contain heavy rare earth elements, the heavy rare earth plated in step (1) is the source of the heavy rare earth elements in the final diffusion magnet, and the mass ratio of the plated heavy rare earth is 0.2% to 4% of the magnet substrate, and the content of the heavy rare earth after grain boundary diffusion is 0.11% to 4%.

[0020] However, when the sintered NdFeB magnet substrate itself contains carbon elements, the mass ratio of the carbon film coated in step (1) needs to meet the carbon content of 0.05% to 0.30wt% in the magnet after grain boundary diffusion.

[0021] When the sintered NdFeB magnet substrate itself contains heavy rare earth elements, the mass ratio of the plated heavy rare earth in step (1) needs to meet the content of the heavy rare earth elements Dy or Tb of 0.11% to 4% in the magnet after grain boundary diffusion.

[0022] Generally, the content of carbon or heavy rare earth in the designed diffusion magnet can be subtracted from the content of carbon or heavy rare earth in the substrate itself, and then the content of carbon or heavy rare earth lost in diffusion can be added to obtain the mass ratio of the carbon film or plated heavy rare earth in step (1). This is a calculation method known to those skilled in the art.

[0023] In step (2), the diffusion temperature is preferably 850°C to 920°C, and the diffusion time is preferably 6h to 12h, more preferably 9 to 12h.

[0024] In step (2), the heating rate of the grain boundary diffusion is preferably 1-10°C / min, more preferably 5-8°C / min.

[0025] In step (2), the tempering temperature is 400°C to 800°C, preferably 400 to 500°C, and the tempering time is 0.2h to 24h, preferably 3h to 6h.

[0026] The application also provides a high-performance sintered NdFeB magnet prepared by the above method, wherein the carbon content is 0.05wt% to 0.3wt%, and the carbon content decreases from the outer layer to the inner layer, and the mass content of heavy rare earth after grain boundary diffusion is 0.11% to 4%.

[0027] Further, in the high-performance sintered NdFeB magnet, the carbon content gradually decreases from the outer layer to the inner layer within a range of 5mm from the outer surface to the inside, and the average carbon content in the grain boundary is much higher than the average carbon content in the grain, and the magnet has this phenomenon at least 5mm from the surface to the inside, i.e. the upper part to the lower part 10mm.

[0028] In the phenomenon that the average carbon content in the grain boundary is much higher than the average carbon content in the grain, the average carbon content in the grain boundary is more than 50% higher than the average carbon content in the grain, more preferably more than 70%.

[0029] The carbon content gradually decreases from the outer layer to the inner layer of the magnet, and the decrease range is between 40-100 ppm / 5 mm.

[0030] Further, the present application provides a high-performance sintered NdFeB magnet, the magnet composition is R1RhM1M2C1A1T1, wherein R1 is one or several of Nd, Pr, Ho, Gd, the content is 27-33 wt% (preferably 28.5-32 wt%), Rh is a heavy rare earth element, which is Dy or Tb, the content is 0.11%-4%; M1 is selected from one or several of Al, Cu, Zn, Sn, In, Ti, V, the content is 0.1-1.5 wt% (preferably 0.2-0.5 wt%), M2 is selected from one or several of Co, Mn, Ni, Ca, Zr, Ga, Nb, Mo, Si, the content is 0.5%-1.5 wt% (preferably 0.70-1.20 wt%), A1 is boron, the content is 0.5%-1.5 wt% (preferably 0.8-1.2 wt%), C1 is carbon, the content is 0.05%-0.3 wt%, and the balance is T1, T1 is Fe.

[0031] The carbon content gradually decreases from the outer layer to the inner layer of the magnet, and the decrease range is between 40-100 ppm / 5 mm.

[0032] The carbon content gradually decreases from the outer layer to the inner layer of the magnet, and the decrease range is between 40-100 ppm / 5 mm.

[0033] In the phenomenon that the average carbon content in the grain boundary is much higher than the average carbon content in the grain, the average carbon content in the grain boundary is more than 50% higher than the average carbon content in the grain, and more preferably more than 70% higher.

[0034] Further, the high-performance sintered NdFeB magnet is prepared by the following method:

[0035] A. Preparation of magnet base:

[0036] According to the component ratio, the raw materials of each element of the magnet base are taken, and after melting and casting, a flake is obtained; the flake is subjected to hydrogen breaking and air flow grinding to obtain a powder, and the powder is pressed and sintered in vacuum to obtain a magnet blank as a base for standby

[0037] B. Diffusion source coating:

[0038] A carbon film is coated on the surface of the magnet base by a multi-arc sputtering method, the thickness of the carbon film is 2-20 um (preferably 5-12 um), the mass ratio of the carbon film to the magnet base is 0.2%-2.0% (preferably 0.89%-1.15%), the magnet steel coated with the carbon film is subjected to magnetron sputtering coating by a plasma vacuum coating machine, and a heavy rare earth film is coated on the magnet steel, the heavy rare earth is Dy or Tb, the thickness of the heavy rare earth film is 1 um-30 um (preferably 5-25 um), the mass ratio of the heavy rare earth to the magnet base is 0.2%-4% (preferably 0.5%-3.0%), and a coated magnet is obtained.

[0039] The PVD target of the multi-arc sputtering method is a graphite target, and the atmosphere is high-purity Ar.

[0040] The magnetron sputtering coating is physical vapor deposition, the atmosphere source is high-purity Ar, the cavity vacuum degree is 0.3-0.5 Pa, the internal working temperature is 100°C-150°C, the thickness of the obtained film layer is 1 um-30 um, the mass ratio of the heavy rare earth is 0.2%-4%, preferably 0.5%-3.0% of the magnet base, and more preferably 1.7%-2.4%.

[0041] C, diffusion treatment:

[0042] The obtained magnet steel B is subjected to grain boundary diffusion treatment, the diffusion temperature is 800°C-1000°C (preferably 850°C-920°C), the diffusion time is 1 h-48 h (preferably 6 h-12 h), the vacuum degree is 1.0*10-3 Pa or more, the heating rate is 1-10°C / min (preferably 5-8°C / min), after the grain boundary diffusion, the magnet steel is cooled to room temperature and then subjected to tempering treatment, the tempering temperature is 400°C-800°C (preferably 400-500°C), and the tempering time is 0.2 h-24 h (preferably 3 h-6 h), thereby obtaining the high-performance sintered NdFeB magnet.

[0043] In the magnet composition, the total amount of Nd and Pr in R1 is preferably more than 50% of R1, and more preferably more than 80% of R1.

[0044] The total amount of Al and Cu in M1 is preferably more than 55% of M1, and more preferably more than 85% of M1; and the amount of Cu is more than 15% of M1, and more preferably more than 30% of M1.

[0045] The total amount of Co, Ga, and Zr in M2 is preferably more than 55% of M2, and more preferably more than 85% of M2; and the amount of Ga is more than 5% of M2, and more preferably more than 10% of M2.

[0046] In step B, when the magnet base contains carbon elements, the mass ratio of the coated carbon film needs to satisfy that the carbon content in the magnet after the grain boundary diffusion treatment is 0.05%-0.30 wt%.

[0047] In step B, when the magnet base contains heavy rare earth elements, the mass ratio of the heavy rare earth plated in step (1) needs to meet the content of the heavy rare earth elements Dy or Tb in the magnet after the grain boundary diffusion is 0.11% to 4%.

[0048] The application also provides a preparation method of the high-performance sintered NdFeB magnet, and the method comprises the following steps:

[0049] A. Preparation of a magnet base:

[0050] According to the component proportion, the raw materials of each element of the magnet base are taken, and a flake is obtained after smelting and casting; the flake is subjected to hydrogen breaking and airflow grinding to obtain a powder, and the powder is pressed and formed and vacuum sintered to obtain a magnet blank as a base for standby

[0051] B. Diffusion source coating:

[0052] A carbon film with a thickness of 2 to 20 um (preferably 5 to 12 um) and a mass ratio of 0.2% to 2.0% (preferably 0.89% to 1.15%) of the magnet base is coated on the surface of the magnet base by using a multi-arc sputtering method, and the magnet steel coated with the carbon film is subjected to magnetron sputtering coating by using a plasma vacuum coating machine to coat a heavy rare earth film, the heavy rare earth is Dy or Tb, the thickness of the heavy rare earth film layer is 1 um to 30 um (preferably 5 to 25 um), the mass ratio of the heavy rare earth is 0.2% to 4% (preferably 0.5% to 3.0%) of the magnet base, and a coated magnet is obtained.

[0053] The PVD target material of the multi-arc sputtering method is a graphite target material, and the atmosphere is high-purity Ar.

[0054] The magnetron sputtering coating is physical vapor deposition, the atmosphere source is high-purity Ar, the cavity vacuum degree is between 0.3 and 0.5 pa, the internal working temperature is between 100 DEG C and 150 DEG C, the obtained film thickness is between 1 um and 30 um, the mass ratio of the heavy rare earth is between 0.2% and 4%, preferably 0.5% to 3.0% of the magnet base, and more preferably 1.7% to 2.4%.

[0055] C. Diffusion treatment:

[0056] The obtained magnetic steel B is subjected to grain boundary diffusion treatment, the diffusion temperature is 800-1000 DEG C (preferably 850-920 DEG C), the diffusion time is 1-48 h (preferably 6-12 h), the vacuum degree is above 1.0*10-3 Pa, the heating rate is 1-10 DEG C / min (preferably 5-8 DEG C / min), after the grain boundary diffusion, the temperature is cooled to room temperature and then is subjected to tempering treatment, the tempering temperature is 400-800 DEG C (preferably 400-500 DEG C), the tempering time is 0.2-24 h (preferably 3-6 h), thereby the high-performance sintered NdFeB magnet is prepared.

[0057] In the step B, when the magnet substrate contains carbon elements, the mass ratio of the carbon film needs to meet the carbon content of 0.05%-0.30wt% in the magnet after the grain boundary diffusion.

[0058] In the step B, when the magnet substrate contains heavy rare earth elements, the mass ratio of the heavy rare earth plated in the step (1) needs to meet the content of the heavy rare earth elements Dy or Tb of 0.11%-4% in the magnet after the grain boundary diffusion.

[0059] In the application, the grain boundary diffusion is carried out in a vacuum tube furnace, the temperature is raised in a segmented manner, and the cooling mode is vacuum air cooling.

[0060] The applicant finds, through a large number of researches combined with performance tests, that adding a carbon film in the diffusion has a certain influence on the performance of the magnet after the diffusion, and it can be known from the Nd-C phase diagram that the melting point of Nd decreases with the increase of the carbon content, so the addition of carbon is beneficial to reduce the melting point of the Nd-rich phase, and the diffusion mechanism is that the heavy rare earth enters the magnet interior through the diffusion channel, and the diffusion channel is formed by the melting of the Nd-rich phase, so the Nd-rich phase with low melting point can form the diffusion channel earlier, and the diffusion effect is better.

[0061] Therefore, the addition of carbon is beneficial to the earlier formation of the diffusion channel and is beneficial to the diffusion and the improvement of the magnetic performance. Meanwhile, the low diffusion temperature is beneficial to reducing the diffusion of the heavy rare earth into the main phase, thereby reducing the reduction of the remanence after the diffusion, and realizing the magnet with high remanence and high coercive force. However, in the conventional sintering process, if the amount of the added carbon is not artificially controlled, the excessively high sintering temperature will introduce excessive impurity carbon, which will cause performance degradation. Meanwhile, the excessive carbon will also enter the gap between the main phases and react with the main phases, resulting in a large reduction of Br, so the addition amount of the diffusion carbon needs to be appropriate to achieve the best diffusion effect. If the magnet substrate itself contains carbon elements, when the carbon content increases, the C compound in the grain boundary will increase greatly, the Nd-rich phase will be damaged greatly, the grain boundary phase is difficult to flow, and the Hcj improvement amount is not high and the Br reduction amount is larger, so the C content in the prepared magnet should be controlled to be within 0.30%.

[0062] The application has the beneficial effect that by covering the surface of the magnet with a carbon film, controlling the weight of the carbon, and then performing heavy rare earth grain boundary diffusion, the Br reduction is reduced while the heavy rare earth diffusion effect is improved, and finally a high-Br, high-Hcj rare earth NdFeB magnet with high magnetic performance is obtained. BRIEF DESCRIPTION OF DRAWINGS

[0063] Figure 1 The carbon content curve of the magnet of different embodiments is detected every 1mm depth from the outside to the inside.

[0064] Figure 2 The SEM graph of the C content difference of the grain boundary and the grain of the magnet prepared in Example 3 at a depth of 5mm from the outer surface.

[0065] Figure 3 The SEM graph of the C content difference of the grain boundary and the grain of the magnet prepared in Example 3 at a depth of 1mm from the outer surface. DETAILED DESCRIPTION

[0066] The technical solutions of the application will be further described below with specific embodiments, but the protection scope of the application is not limited thereto.

[0067] Example 1:

[0068] First, the substrate is prepared, then a carbon film is plated by magnetron sputtering, and then a pure Tb film is plated. After the film is plated, it is placed in a vacuum tube furnace for diffusion, and the specific steps are as follows:

[0069] The magnet composition of R1RhM1M2C1A1T1, wherein R1 is Nd and Pr, Rh is Tb, the mass ratio is 22.33%, 7.12%, and 0.11% respectively, M1 is selected from Al and Cu, the mass ratio is 0.17% and 0.101% respectively, M2 is selected from Co, Zr, and Ga, the mass ratio is 0.49%, 0.096%, and 0.139% respectively, A1 is boron, the content is 0.96%, C1 is carbon, the content is 0.05%, and the balance is T1 which is Fe.

[0070] The preparation method is as follows:

[0071] S1: Preparation of R1M1M2BFe matrix, the matrix is selected as follows: R1 is Nd+Pr, the mass ratio is 22.33% and 7.12% respectively, M1 is Al and Cu, the mass ratio is 0.17% and 0.101% respectively, M2 is Co, Ca and Zr, the mass ratio is 0.49%, 0.096% and 0.139% respectively, the content of B is 0.96%, and the rest is Fe. According to the component ratio, the raw materials of R1, M1, M2, B and T1 are taken to obtain a spool after melting and casting. The spool is sintered into a blank by hydrogen breaking, airflow grinding, pressing and vacuum sintering. The blank is cleaned and then wire cut. In order to facilitate the detection of magnetic properties and composition, the magnet is cut into several Φ10*10mm magnetic steels A. The magnetic steels A are crushed and sampled in the center. The composition of the magnet is detected by ICP-MS OES. The results are shown in Table 1.

[0072] S2: Magnetron sputtering coating of diffusion source is carried out. A layer of carbon film is coated on the Φ10mm*10mm magnetic steel A by multi-arc sputtering method, the thickness of the carbon film layer is 1.7um, and the mass ratio is 0.20%. Then, Tb film is plated on the magnetic steel B by magnetron sputtering physical vapor deposition in the plasma vacuum coating machine. The atmosphere source is high-purity Ar, the cavity vacuum degree is between 0.3-0.5pa, the internal working temperature is 120℃, the thickness of the Tb film layer is 15um, and the mass ratio of terbium is about 1.7%.

[0073] S3: Diffusion treatment: the obtained magnetic steel B is put into the boat and enters the vacuum tube furnace for diffusion treatment. The diffusion treatment is divided into two groups. One group is treated at a temperature of 905℃ for 9h, and the other group is treated at a temperature of 905℃ for 6h. The vacuum degree is above 1.0*10-3Pa, the heating rate of the vacuum tube furnace is 6.5℃ / min, the tempering temperature is 445℃, and the tempering time is 4.5h.

[0074] S4: The obtained magnet is tested for magnetic properties, then subjected to sand blasting demagnetization treatment, and tested for composition from the outside to the inside. The C content is tested by high-frequency infrared carbon and sulfur analyzer. The test method is to cut the magnet every 1mm in thickness from the outside to the inside, then perform sand blasting treatment and composition test. The composition of the magnet is measured by ICP-OES. The results are shown in Table 2. Figure 1 .

[0075] NIM15000 is used to measure the magnetic properties of the magnet at 20℃±3℃. SEM and EPMA are used to analyze the microstructure and micro-area composition of the magnet.

[0076] Example 2:

[0077] The preparation method is the same as that of Example 1, except that the weight ratio of the diffusion source graphite is 0.55%.

[0078] Example 3:

[0079] The same as the preparation method of Example 1, except that the weight percentage of the diffusion source graphite is 0.89%.

[0080] Example 4:

[0081] The same as the preparation method of Example 1, except that the weight percentage of the diffusion source graphite is 1.05%.

[0082] Example 5:

[0083] The same as the preparation method of Example 1, except that the weight percentage of the diffusion source graphite is 1.15%.

[0084] Example 6:

[0085] The same as the preparation method of Example 1, except that the weight percentage of the diffusion source graphite is 1.53%.

[0086] Example 7:

[0087] The same as the preparation method of Example 1, except that the weight percentage of the diffusion source graphite is 2.0%.

[0088] Example 8:

[0089] The same as the preparation method of Example 4, except that the weight percentage of the diffusion source terbium is 2.03%.

[0090] Example 9:

[0091] The same as the preparation method of Example 4, except that the weight percentage of the diffusion source terbium is 2.40%. The control group goes through steps S1, S3, and S4, but does not go through the S2 diffusion step.

[0092] The composition of the magnetic steel a is as shown in Table 1:

[0093] Table 1

[0094]

[0095]

[0096] The performance after diffusion treatment is as shown in Table 2.

[0097] Table 2

[0098]

[0099]

[0100] The performance of the control group is as shown in Table 3

[0101] Table 3

[0102]

[0103] The SEM image of the difference of C content in the grain boundary and the grain of the magnet prepared in Example 3 from the surface 5mm deep is shown in Figure 2, and the content data of C and other elements corresponding to different positions in the image are shown in Table 4. Figure 2

[0104] Table 4

[0105]

[0106] The SEM image of the difference of C content in the grain boundary and the grain of the magnet of Example 3 from the surface 1mm deep is shown in Figure 3, and the content data of C and other elements corresponding to different positions in the image are shown in Table 5. Figure 3

[0107] Table 5

[0108]

[0109]

[0110] From the above figures and tables, the following conclusions are drawn:

[0111] 1. Figure 1 It is concluded that the average C content gradually decreases from the outer surface to the inside, and the range of decrease is between 40-100ppm / 5mm.

[0112] 2. Figure 2 , 3 , Tables 4 and 5 show that from the surface of the magnet to the inside, the closer to the surface, the higher the C content in the grain boundary phase, and the farther from the surface, the lower the C content. Meanwhile, the weight ratio of C in the grain boundary phase is much higher than that in the grain, and the C content in the grain boundary phase is more than 70% higher than the average C content in the grain, which is beneficial to improve the diffusion effect and significantly increase the magnetic properties.

[0113] From the comparison of Tables 2 and 3, Examples 1-7 and Comparative Examples 905℃*6h and 905*9h, it is concluded that the method of the present application can greatly improve the magnetic properties of the magnet, and it is also shown that the addition of an appropriate amount of graphite reduces the melting point of the Nd-rich phase, so that the diffusion channel is formed earlier, which not only prevents the diffusion of heavy rare earths to the main phase, but also increases the diffusion depth of heavy rare earths, thereby reducing the decrease in Br and increasing the increase in Hcj, and improving the overall diffusion effect.

[0114] Example 10:

[0115] The preparation method is the same as that of Example 4, except that the diffusion temperature is 850℃ and the time is 9h. ​​

[0116] The control group 10 is prepared by the same method as the example, except that there is no diffusion step of the graphite layer in S2, but there is a diffusion step of Tb.

[0117] Example 11 is prepared by the same method as Example 4, except that the diffusion temperature is 920°C and the time is 9h.

[0118] The control group 11 is prepared by the same method as the example, except that there is no diffusion step of the graphite layer in S2, but there is a diffusion step of Tb.

[0119] Table 6 Performance of Example 10, 11 and control group

[0120]

[0121] Conclusion:

[0122] Table 6 shows that after adding the graphite diffusion source, compared with high diffusion temperature, low diffusion temperature is beneficial to reduce the diffusion of heavy rare earth into the main phase, thereby reducing the reduction of remanence after diffusion, realizing the high remanence and coercivity of the magnet, and the reduction of squareness is also small.

[0123] Example 12

[0124] The preparation method is the same as Example 4, except that the composition of the substrate is different, the substrate contains Tb component, and the specific composition is shown in Table 7. In Example 12, the diffusion source Tb is 30nm in film thickness, and the mass accounts for 4.0wt% of the magnet, the diffusion time is 36h, and the rest is the same as Example 4.

[0125] Example 13 is prepared by the same method as Example 12, except that the mass of the diffusion source Tb accounts for 3.8wt% of the body,

[0126] Example 14 is prepared by the same method as Example 12, except that the mass of the diffusion source Tb accounts for 3.5wt% of the magnet,

[0127] Example 15 is prepared by the same method as Example 12, except that the diffusion time is 24h, and the rest is the same.

[0128] Example 16 is prepared by the same method as Example 12, except that the diffusion time is 12h, and the rest is the same.

[0129] The control group is the performance of the substrate.

[0130] Table 7 Composition of the substrate in Examples 12-16 and content of the composition after diffusion (wt%)

[0131] Group Nd Pr B Al Co Cu Ga Tb Zr Fe Example 12 19.00 6.10 0.95 0.15 1.17 0.10 0.18 4.30 0.10 67.65 Example 13 19.50 6.10 0.95 0.15 1.16 0.10 0.18 4.10 0.10 67.85 Example 14 19.80 6.10 0.95 0.15 1.17 0.10 0.18 4.00 0.10 67.65 Example 15 21.10 6.10 0.95 0.15 1.16 0.10 0.18 2.80 0.10 67.36 Example 16 23.00 6.10 0.95 0.15 1.16 0.10 0.18 1.30 0.10 66.96 Matrix 23.80 6.20 0.10 0.16 1.18 0.10 0.18 0.90 0.10 67.28

[0132] Table 8 Performance of Examples 12-16 and control group

[0133]

[0134] Conclusions:

[0135] As can be seen from Examples 12-16

[0136] 1. The extension of the diffusion temperature causes the Nd-rich phase to evaporate in large quantities, the Nd content to decrease greatly, the Br to decrease greatly, the Tb diffusion amount to increase greatly, and the Hcj to increase significantly.

[0137] 2. After the Tb content exceeds 4 wt% after diffusion, the Br and SQ decrease greatly, and the Br decrease is uncontrollable. Therefore, the amount of Tb after diffusion is controlled to be within 4.0 wt%, so as to achieve a small decrease in Br and a high increase in Hcj.

[0138] Example 17 has the same preparation method as Example 4, except that the composition of the substrate is different, as shown in Table 8. The diffusion time is 9 h.

[0139] Example 18 has the same preparation method as Example 17, except that the content of the diffusion source Tb is 2.8 wt%.

[0140] Example 19 has the same preparation method as Example 17, except that the content of the diffusion source Tb is 3.2 wt%.

[0141] Example 20 has the same preparation method as Example 17, except that the content of the diffusion source Tb is 0.2 wt%.

[0142] The control group is the performance of the substrate.

[0143] Table 9: Composition of the substrate in Examples 17-20 and the content of the composition after diffusion (wt%)

[0144] Nd Pr B Co Cu Ga Tb Zr Fe Example 17 19.30 6.10 0.90 0.79 0.13 0.24 3.99 0.085 68.465 Example 18 19.10 6.10 0.90 0.80 0.14 0.24 4.10 0.086 68.534 Example 19 19.00 6.10 0.90 0.78 0.13 0.24 4.15 0.088 68.612 Example 20 19.48 6.20 0.90 0.80 0.14 0.24 3.81 0.088 68.42 Matrix 19.50 6.20 0.90 0.80 0.14 0.24 3.80 0.088 68.42

[0145] Table 10: Performance of Examples 17-20 and the control group

[0146]

[0147] Conclusions:

[0148] According to Table 9 and Table 10, when the substrate of the magnet has a high Tb content, the Hcj increase is not as obvious as before when the Tb content after diffusion is higher than 4.0 wt%. Therefore, it is better to control the diffusion amount of Tb element after diffusion to be within 4.0 wt%.

[0149] Example 21 has the same preparation method as Example 7, except that 0.05% of carbon is added in the form of double-alloy mixing in the substrate. The diffusion time is 9 h.

[0150] Example 22 was prepared in the same manner as Example 7 except that 0.10% carbon was added to the matrix by double alloying.

[0151] Example 23 was prepared in the same manner as Example 7 except that 0.15% carbon was added to the matrix by double alloying.

[0152] Example 24 was prepared in the same manner as Example 7 except that 0.20% carbon was added to the matrix by double alloying.

[0153] Example 25 was prepared in the same manner as Example 7 except that 0.25% carbon was added to the matrix by double alloying.

[0154] Example 26 was prepared in the same manner as Example 7 except that 0.30% carbon was added to the matrix by double alloying.

[0155] The control group was the matrix performance.

[0156] Table 11 Carbon content after diffusion and magnetic properties after diffusion of Examples 21-26 and the control group performance

[0157] Br / KGs Hcj / KOe HK / Hcj Carbon content / wt% Control 21 14.72 14.73 0.98 0.05 Control 22 14.71 14.71 0.98 0.10 Example 21 14.28 22.51 0.97 0.18 Example 22 14.23 20.91 0.97 0.23 Example 23 14.18 20.91 0.97 0.27 Example 24 14.11 21.21 0.96 0.30 Example 25 13.95 15.92 0.94 0.34 Example 26 13.73 15.56 0.93 0.37

[0158] Conclusion: When the carbon content increases from 0.18wt% to 0.37wt%, the Hcj increases gradually, and the Br decreases gradually. Through research, it is found that the increase of carbon content leads to the increase of C compounds in the grain boundary and the destruction of the rich Nd phase. The grain boundary phase is difficult to flow, especially after 0.30wt%, the Hcj increase is not high, and the Br decrease is more. Therefore, the C content in the prepared magnet should be controlled within 0.30%.

Claims

1. A diffusion process for improving the magnetic properties of sintered magnets, characterized by The method comprises the following steps: (1) covering a carbon film on the surface of the sintered NdFeB magnet substrate by using a multi-arc sputtering method, the thickness of the carbon film is 2-20 um, the mass ratio is 0.2%-2.0% of the magnet substrate, the magnet substrate coated with the carbon film is subjected to magnetron sputtering plating, and a heavy rare earth film is plated, the thickness of the heavy rare earth film layer is 1 um-30 um, the mass ratio of the heavy rare earth is 0.2%-4% of the magnet substrate, and a plated magnet is obtained; the mass ratio of the carbon film and the mass ratio of the heavy rare earth need to meet that, after grain boundary diffusion, the carbon content in the magnet is 0.05%-0.30 wt%, and the content of the heavy rare earth after the grain boundary diffusion is 0.11%-4%; (2) The plated magnet is subjected to grain boundary diffusion treatment, the diffusion temperature is 850-905 ℃, the diffusion time is 6-12 h, and the vacuum degree is 1.0*10 -3 Pa, after the grain boundary diffusion, the magnet is cooled to room temperature and then reheated for tempering treatment, thereby obtaining the high-performance sintered NdFeB magnet after the grain boundary diffusion.

2. The method of claim 1, wherein In the step (1), the heavy rare earth is Tb or Dy.

3. The method of claim 1, wherein In the step (2), the tempering temperature is 400-800 DEG C, and the tempering time is 0.2-24 h.

4. The high-performance sintered NdFeB magnet prepared by the method according to any one of claims 1-3, characterized in that In the magnet, the carbon content is 0.05%-0.30 wt%, and the carbon content decreases from the outer layer to the inner layer of the magnet, and the mass content of the heavy rare earth after the grain boundary diffusion is 0.11%-4%.

5. The high performance sintered NdFeB magnet of claim 4, wherein In the magnet, within a range of 5 mm from the outer surface to the inside, the carbon content gradually decreases from the outside to the inside, and the average carbon content in the grain boundary is more than 50% higher than the average carbon content in the grain.

6. A high performance sintered NdFeB magnet, characterized by The magnet component is R1R h M1M2C1A1T1, wherein R1 is one or several of Nd, Pr, Ho, Gd, the content of which is 27-33wt%, R h is a heavy rare earth element, is Dy or Tb, the content of which is 0.11%-4%; M1 is selected from one or several of Al, Cu, Zn, Sn, In, Ti, V, the content of which is 0.1-1.5wt%, M2 is selected from one or several of Co, Mn, Ni, Ca, Zr, Ga, Nb, Mo, Si, the content of which is 0.5%-1.5wt%, A1 is boron, the content of which is 0.5%-1.5wt%, C1 is carbon, the content of which is 0.05%-0.30wt%, and the balance is T1, T1 being Fe; In the magnet, within a range of 5 mm from the outer surface to the inside, the carbon content gradually decreases from the outside to the inside, and the average carbon content in the grain boundary is much higher than the average carbon content in the grain. In the phenomenon that the average carbon content in the grain boundary is much higher than the average carbon content in the grain, the average carbon content in the grain boundary is more than 50% higher than the average carbon content in the grain.

7. The high performance sintered NdFeB magnet of claim 6, wherein The magnet is prepared by the following method: A, preparation of a magnet substrate: According to the component allocation ratio, the raw materials of each element of the magnet substrate are taken, the castings are obtained after melting and casting, the castings are subjected to hydrogen breaking and airflow grinding to obtain powder, the powder is pressed and formed, and vacuum sintering is performed to obtain a magnet blank as a substrate for standby; B, diffusion source plating: A carbon film is covered on the surface of the magnet substrate by using a multi-arc sputtering method, the thickness of the carbon film is 2-20 um, the mass ratio is 0.2%-2.0% of the magnet substrate, the magnet coated with the carbon film is subjected to magnetron sputtering plating, and a heavy rare earth film is plated, the thickness of the heavy rare earth film layer is 1 um-30 um, the mass ratio of the heavy rare earth is 0.2%-4% of the magnet substrate, and a plated magnet is obtained; C, diffusion treatment: The magnet obtained in step B is subjected to grain boundary diffusion treatment at a diffusion temperature of 800-1000℃, a diffusion time of 1-48h, and a vacuum degree of 1.0*10 -3 The temperature is raised at a rate of 1-10℃ / min, and after the grain boundary diffusion, the temperature is cooled to room temperature and then raised for tempering treatment at a tempering temperature of 400-800℃ and a tempering time of 0.2-24h, to obtain the high-performance sintered NdFeB magnet.

8. A method for producing the high-performance sintered NdFeB magnet as claimed in claim 6, characterized by The method is: A, preparation of a magnet substrate: According to the component allocation ratio, the raw materials of each element of the magnet substrate are taken, the castings are obtained after melting and casting, the castings are subjected to hydrogen breaking and airflow grinding to obtain powder, the powder is pressed and formed, and vacuum sintering is performed to obtain a magnet blank as a substrate for standby; B, diffusion source plating: A carbon film is covered on the surface of the magnet substrate by using a multi-arc sputtering method, the thickness of the carbon film is 2-20 um, the mass ratio is 0.2%-2.0% of the magnet substrate, the magnet coated with the carbon film is subjected to magnetron sputtering plating, and a heavy rare earth film is plated, the thickness of the heavy rare earth film layer is 1 um-30 um, the mass ratio of the heavy rare earth is 0.2%-4% of the magnet substrate, and a plated magnet is obtained; C. Diffusion treatment: The magnet obtained in step B is subjected to grain boundary diffusion treatment at a diffusion temperature of 800-1000℃, a diffusion time of 1-48h, and a vacuum degree of 1.0*10 -3 The temperature is raised at a rate of 1-10℃ / min, and after the grain boundary diffusion, the temperature is cooled to room temperature and then raised for tempering treatment at a tempering temperature of 400-800℃ and a tempering time of 0.2-24h, to obtain the high-performance sintered NdFeB magnet.

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